1. Field of the Invention
This invention relates to a 1-phase energized disk-type brushless motor having a single position detecting element, and more particularly to a 1-phase energized disk-type axial-flow brushless fan motor having a single position detecting element.
2. Description of the Prior Art
As various systems have been developed, brushless motors, especially disk-type brushless motors, suitable for use with such systems, have been required. Disk-type brushless motors can be used as axial-flow brushless fan motors which are widely used in office machines and the like, and in some applications, are required to be very inexpensive, small and very thin, not to mention the rotational efficiency (naturally, the rotational efficiency must be higher than a particular lever in order that they may be of practical use as such).
Those motors which meet the requirements best are 1-phase energized disk-type brushless motors which include a single armature coil and a single position detecting element. In such 1-phase energized disk-type brushless fan motors, a field magnet is used as a rotor and is disposed for relative rotation in a face-to-face opposing relationship to a stator armature having one or more armature coils thereon. However, such a mere 1-phase energized disk-type brushless motor cannot actually operate as a motor because it cannot rotate continuously, although the magnet rotor can turn over a predetermined range. Otherwise, even if a motor having a single armature coil and a single position-detecting element can rotate continuously, the single armature coil could not provide a sufficiently strong turning force. Therefore, for a sufficient turning force, two or more armature coils must necessarily be provided for a motor.
A disk-type brushless motor having two armature coils for a stator armature normally requires two or more position-detecting elements. In most cases, magnetoelectric transducers such as Hall elements or Hall ICs (integrated circuits) are used for the position-detecting elements. However, since such position-detecting elements are expensive, it is desirable for a motor to include, if possible, only one position-detecting element in order that inexpensive, small disk-type brushless motors can be mass produced. However, such a motor having a single position-detecting element has a drawback that, where armature coils are arranged at same-phase positions for a single phase, it cannot start itself if the position-detecting element detects a boundary between the N (north) pole and the S (south) pole of the magnet rotor, that is, a dead point, and similarly in a motor having a single coil as described above.
Where a motor has armature coils arranged for two phases, it requires two position-detecting elements and therefore driver circuits for the two phases, resulting in increased cost.
Thus, in order for a motor to contain a single position detecting element, it must be a 1-phase energized brushless motor.
Further, a 1-phase energized brushless motor is very advantageous where it is used particularly as an axial-flow brushless fan motor. Accordingly, it is desirable for a motor to contain only one position-detecting element which is very expensive and only one driver circuit for a single phase.
Accordingly, in a 1-phase energized brushless motor, in order that the motor may be produced at a low cost and rotated continuously with only one position-detecting element contained therein, it is designed such that the rotor may be positioned, upon stopping and starting, normally at a position other than a dead point so as to utilize a cogging torque to assure self-starting of the motor. More particularly, a 1-phase or single phase motor has a dead point at an energization switching point at which the motor provides zero or no torque. Therefore, the 1-phase motor has a drawback that it cannot start itself if the rotor position upon starting of the motor is just at a dead point.
Therefore, a 1-phase motor is normally provided with a cogging generating magnetic member (an iron piece is used therefor) for generating a torque (cogging torque) in addition to a torque generated by an armature coil and a field magnet (rotor magnet) in order to eliminate such dead points to allow self-starting of the motor.
In a coreless brushless motor, for example, the following methods for generating a cogging torque are known. Referring first to FIG. 1, a 6-pole field magnet or magnet rotor 2 having an alternate arrangement of the 6 north and south poles is mounted on a rotor yoke 1 in an opposing relationship to a stator yoke 5 with an air gap 4 left therebetween and with a pair of coreless armature coils 3 disposed in the air gap 4. In the motor of FIG. 1, the stator yoke 5 has at a face thereof opposing the field magnet 2 two inclined surfaces which thus define the complementarily inclined air gap 4. This method, however, has a drawback that the efficiency is relatively low because the air gap is relatively great. Besides, it is troublesome to form such inclined surfaces on a face of a stator yoke.
Referring now to FIG. 2, another method is illustrated. In the motor of FIG. 2, a stator yoke 5 has no such inclined faces as provided on the stator yoke 5 of FIG. 1. Instead, an iron bar 6 is mounted on the stator yoke 5 and extends through each of a pair of coreless armature coils 3 disposed in a uniform air gap 4 defined by the stator yoke 5 and a field magnet or magnet rotor 2 on a rotor yoke 1. According to this arrangement, a magnetic flux will appear as seen in FIG. 3, and hence the field magnet 2 will stop at a position in which the iron bars 6 are each opposed to the center of one of the N and S poles of the field magnet 2. Accordingly, if the armature coils 3 are located so as to produce a rotational torque in such a stopping position of the field magnet 2, a coreless brushless motor which can start itself will be obtained.
However, the method as shown in FIG. 2 has a drawback that if the thickness of the iron bars 6 is increased in order to increase the cogging torque, to assure that the motor can be started more certainly by itself, a phenomenon that the torque around dead points decreases will appear because a magnetic flux 7 will act as shown in FIG. 4 around the dead points.
In order to obtain an ideal torque--angular rotor displacement curve, it is necessary to obtain a composite torque curve 8 as shown in FIG. 5. In FIG. 5, an armature coil torque curve by an armature coil is indicated by a curve 9 while a cogging torque curve by a cogging generating magnetic member is indicated by a curve 10. As apparent from the armature coil torque curve 9 and the cogging torque curve 10, the cogging torque should be a half of the armature torque in magnitude. Accordingly, the torque curve 8 composite of the armature coil torque and the cogging torque exhibits a substantially uniform rotational torque over the entire range of rotation.
In order to obtain such an ideal composite torque curve 8, a cogging magnetic member must be designed correctly in size and location, and the present invention can provide such an ideal composite torque curve 8.
Thus, the present applicant already proposed and applied for a patent a disk-type brushless motor wherein a cogging torque having a sufficient magnitude and presenting an ideal torque-angular rotor displacement curve can be produced. Now, the disk-type brushless motor of the preceding patent application will be described with reference to FIGS. 6 to 10.
FIG. 6 is a plan view of a 1-phase energized disk-type axial-flow brushless fan motor to which a 1-phase energized disk-type brushless motor is applied, FIG. 7 a vertical sectional view of the motor of FIG. 6, FIG. 8 a bottom plan view of a 6-pole field magnet, FIG. 9 an enlarged vertical sectional view of the stator side of the motor of FIG. 7, and FIG. 10 is a plan view of a stator armature of the motor of FIG. 7.
A disk-type axial-flow brushless fan motor 11 includes a casing 12 made of a plastics material and having a rectangular shape in plan (FIG. 6) and a cup-shaped vertical section (FIG. 7) with an inner spacing 13 formed therein in which a motor device 14 which will be hereinafter described is located. A plurality of stays not shown are formed at the bottom of the spacing 13 and define therebetween inlet windows 16 for passing therethrough a wind caused by a fan blade 15 which will be hereinafter described.
The disk-type axial-flow brushless fan motor 11 further includes a rotor 17 having a plurality of fan blades 15 integrally formed around an outer periphery of a cup-shaped body 18 made of plastic material. The cup-shaped body 18 has a rotor yoke 19 securely mounted on an inner face thereof, and a 6-pole field magnet or magnet rotor 2 is securedly mounted on a lower face of the rotor yoke 19 and has 6 alternate N and S magnet poles magnetized with an equal magnetization angular width as shown in FIG. 8. A rotary shaft 20 is secured at an end thereof to the rotor 17 and supported for rotation adjacent the other end thereof by means of an oilless metal bearing 21.
A printed circut board 22 is supported on the casing 12, and a stator yoke 23 is located on the printed circuit board 22. The stator yoke 23 has securely mounted thereon by a suitable means a cogging generating magnetic member 25 which will be hereinafter described. The stator yoke 23 is provided for closing a magnetic path of the field magnet 2. The stator yoke 23 is processed for insulation on a surface thereof and includes a pair of coreless-type armature coils 29-1, 29-2 fixedly mounted thereon and arranged in a symmetrical relationship relative to the center of the motor 11, that is, in a spaced relationship by an angle of 180 degrees around the center of the motor 11, as shown in FIG. 10. The armature coils 29-1, 29-2 are approximately sector-shaped in plan and each have a pair of radial, magnetically active conductor portions 29a, 29b which contribute to generation of a torque and include therebetween a distance or angular width substantially equal to the angular width of each magnetic pole of the field magnet 2. In particular, because the field magnet 2 has 6 poles and hence the width of each pole thereof is 60 degrees, the width between the magnetically active conductor portions 29a, 29b is 60 degrees. Each of the armature coils 29-1, 29-2 further has a pair of circumferential conductor portions 29c, 29d which do not contribute to generation of a torque.
A position-detecting element 24 composed of a magnetoelectric transducer such as Hall element, a Hall IC (integrated circuit) or a magnetic reluctance element is located at a position circumferentially displaced by an angle substantially equal to the width of each pole of the field magnet 2, that is, by an angle of 60 degrees, from the magnetically active conductor portion 29b of the armature coil 29-1. Accordingly, the position detecting element 24 is arranged at a position intermediate the magnetically active conductor portion 29b of the armature coil 29-1 and the magnetically active conductor portion 29a of the armature coil 29-2.
The cogging generating magnetic member 25 is securely mounted on an upper face of the stator yoke 23 and is in the form of a plate having an angular width substantially equal to the angular width of each pole of the field magnet 2, that is, an angular width of 60 degrees. The cogging generating magnetic member 25 is located on the stator yoke 23 such that the radial center line 27 between the width thereof is at a position spaced by about three fourths of the width of each pole of the field magnet 2, that is, by an angle of 45 degrees, from the magnetically active conductor portion 29b of the armature coil 29-2.
Since the disk-type axial-flow brushless fan motor 11 has such a construction as described above, the field magnet 2 which is mounted for relative rotation in a face-to-face opposing relationship to the armature coils 29-1, 29-2, the position detecting element 24 and the cogging generating magnetic member 29 will stop, upon stopping of the motor 11, at a position wherein the cogging generating magnetic member 25 is attracted by one of the N and S poles of the field motor 2 to enable self-starting of the motor 11. Accordingly, if the power source is thrown in again, since the position detecting element 24 detects an N or S pole of the field magnet 2, the armature coils 29-1, 29-2 are energized in a predetermined direction in response to a signal from the position detecting element 24 to thus generate an armature coil torque in a predetermined direction. Consequently, the rotor 17 having the field magnet 2 thereon is driven to rotate to cause the blades 15 thereon to send a wind through the inlet openings 16. In this manner, a cogging torque is generated due to the presence of the cogging generating magnetic member 25 and causes the rotor 17 to a position other than dead points. Accordingly, an N or S pole of the field magnet 2 will soon be detected by the position-detecting element 24, and hence the rotor 17 can thereafter rotate continuously. Besides, because the cogging generating magnetic member 25 having such a shape as described above is located at such a position as described above, an ideal cogging torque will be generated at an ideal rotational angular position, and hence a rotational torque will be obtained which is substantially uniform over an entire range of rotational angle.
It is to be noted that while the motor described above contains two armature coils, it may otherwise contain one or three or more armature coils therein.
As apparent from the foregoing description, such a coreless, 1-phase energized disk-type brushless motor as described above is very useful in practical use because it can start itself with a single position detecting element, a cogging torque of a sufficient magnitude can be produced, and a rotational torque can be produced which is uniform over an entire range of rotational angle to allow smooth rotation of the motor.
However, according to the disk-type axial-flow brushless fan motor 11 to which such a 1-phase energized brushless fan motor as described above is applied, the cogging generating magnetic member 25 must be secured to the stator yoke 23 after the former has been positioned properly on the latter. Further, there is a drawback which is troublesome and deteriorates the mass-productivity, that although a chip part which is an electric circuitry part constituting an energization controlling circuit must necessarily be located on the printed circuit board 22 having a printed wiring pattern not shown thereon and located at the lower face of the stator yoke 23, the stator yoke 23 must have a cutaway portion 28 and a terminal 16 of the position detecting element 24 on the stator yoke 22 must extend through the cutaway portion 28 of the stator yoke 23 and be connected to a predetermined portion of the printed circuit board 23. It is to be noted here that the position-detecting element 24 does not achieve its function unless it is located in a face-to-face relationship to the field magnet 2. Accordingly, the position-detecting element 24 cannot be located on a lower face of the stator yoke 22.